racy datagram queue may lead to deadlock

[marten-seemann]

Might be related to #3544.

• Failure [0.564 seconds]
Datagram test
/home/circleci/project/integrationtests/self/datagram_test.go:22
  with QUIC version v2
  /home/circleci/project/integrationtests/self/datagram_test.go:26
    sends datagrams [It]
    /home/circleci/project/integrationtests/self/datagram_test.go:111

    Expected
        <int>: 23
    to be >
        <int>: 87

    /home/circleci/project/integrationtests/self/datagram_test.go:144

    Full Stack Trace
    github.com/lucas-clemente/quic-go/integrationtests/self_test.glob..func4.1.4()
    	/home/circleci/project/integrationtests/self/datagram_test.go:144 +0x1165
    github.com/onsi/ginkgo/internal/leafnodes.(*runner).runSync(0xc0040f1440)
    	/home/circleci/go/pkg/mod/github.com/onsi/ginkgo@v1.16.4/internal/leafnodes/runner.go:113 +0xf6
    github.com/onsi/ginkgo/internal/leafnodes.(*runner).run(0xc0040f1440)
    	/home/circleci/go/pkg/mod/github.com/onsi/ginkgo@v1.16.4/internal/leafnodes/runner.go:64 +0x158
    github.com/onsi/ginkgo/internal/leafnodes.(*ItNode).Run(0xc0000af040)
    	/home/circleci/go/pkg/mod/github.com/onsi/ginkgo@v1.16.4/internal/leafnodes/it_node.go:26 +0x95
    github.com/onsi/ginkgo/internal/spec.(*Spec).runSample(0xc003d42ff0, 0xfbf3f8?, {0xcdb240, 0xc0001988c0})
    	/home/circleci/go/pkg/mod/github.com/onsi/ginkgo@v1.16.4/internal/spec/spec.go:215 +0x35a
    github.com/onsi/ginkgo/internal/spec.(*Spec).Run(0xc003d42ff0, {0xcdb240, 0xc0001988c0})
    	/home/circleci/go/pkg/mod/github.com/onsi/ginkgo@v1.16.4/internal/spec/spec.go:138 +0x1ac
    github.com/onsi/ginkgo/internal/specrunner.(*SpecRunner).runSpec(0xc00019c000, 0xc003d42ff0)
    	/home/circleci/go/pkg/mod/github.com/onsi/ginkgo@v1.16.4/internal/specrunner/spec_runner.go:200 +0x15b
    github.com/onsi/ginkgo/internal/specrunner.(*SpecRunner).runSpecs(0xc00019c000)
    	/home/circleci/go/pkg/mod/github.com/onsi/ginkgo@v1.16.4/internal/specrunner/spec_runner.go:170 +0x256
    github.com/onsi/ginkgo/internal/specrunner.(*SpecRunner).Run(0xc00019c000)
    	/home/circleci/go/pkg/mod/github.com/onsi/ginkgo@v1.16.4/internal/specrunner/spec_runner.go:66 +0x137
    github.com/onsi/ginkgo/internal/suite.(*Suite).Run(0xc000020af0, {0x7f7a7c0ce9a0, 0xc003580680}, {0xbe09ab, 0x16}, {0xc00010e1c0, 0x1, 0x1}, {0xce0710, 0xc0001988c0}, ...)
    	/home/circleci/go/pkg/mod/github.com/onsi/ginkgo@v1.16.4/internal/suite/suite.go:79 +0x6f6
    github.com/onsi/ginkgo.runSpecsWithCustomReporters({0xcdb860?, 0xc003580680}, {0xbe09ab, 0x16}, {0xc00009fe48, 0x1, 0x7f7aa4e10008?})
    	/home/circleci/go/pkg/mod/github.com/onsi/ginkgo@v1.16.4/ginkgo_dsl.go:238 +0x213
    github.com/onsi/ginkgo.RunSpecs({0xcdb860, 0xc003580680}, {0xbe09ab, 0x16})
    	/home/circleci/go/pkg/mod/github.com/onsi/ginkgo@v1.16.4/ginkgo_dsl.go:213 +0x268
    github.com/lucas-clemente/quic-go/integrationtests/self_test.TestSelf(0x0?)
    	/home/circleci/project/integrationtests/self/self_suite_test.go:399 +0x105
    testing.tRunner(0xc003580680, 0xc18c88)
    	/usr/local/go/src/testing/testing.go:1439 +0x214
    created by testing.(*T).Run
    	/usr/local/go/src/testin

[marten-seemann]

This is not just a flaky test, this is a race condition in the datagramQueue. NextFrameSize might return protocol.InvalidByteCount (indicating that there's nothing to send), when the next frame isn't queued fast enough in AddAndWait.